Timers for measuring the rate defect of a timepiece have been used for a number of years by watchmakers, other clock repairmen, and clock retailers. (Pertaining to a timepiece herein, by "rate defect" is meant an expression of how fast or slowly it is running with respect to standard time). The first timers to be patented in this country detected the ticking sound (beat) produced by an escapement, converted the sound to an electrical pulse, measured the time between a certain number of these pulses, and then delivered to the operator an indication of rate defect. Examples of such timers are found in U.S. Pat. No. 4,335,596 and 3,926,048, among others.
Given some means of producing an electronic pulse for each period of a clock's movement, the subsequent circuitry for timing the pulses and delivering a display of rate defect may now be called conventional post beat detection circuitry, and for the sequel of this disclosure will be referred to as conventional timing circuitry.
To date in all devices for timing clocks, there is little if any allusion to pendulum clock timers as a separate class. Until a decade ago the dominant type of movement for both watches and pendulum clocks was the mechanical movement. Perhaps this is why pendulum timers have been available only as accessories or extensions to watch timers which work off of an escapement beat.
The usefulness of conventional timers in the case of pendulum clocks has been hampered by the inconvenience of timing a clock which cannot be easily moved and by the less precise performance of beat detectors, when applied to pendulums, than when applied to watches.